Signal processing apparatuses that apply noise suppression and the like after transforming an input signal in(t) into the frequency domain and then apply inverse transform into the time domain to output an output signal out(t) have been known.
In such signal processing apparatuses that are intended for noise suppression and the like, the input signal in(t) is divided into frames, and the input signal in(t) divided into frames is transformed into the frequency domain, and noise suppression and the like is applied in each frame in the frequency domain. Then, inverse transform into the time domain is applied, and a frame signal is generated for each frame. Then, the frame signal for the current frame and the frame signal for the immediately preceding frame are overlapped to generate the output signal out(t).
However, when the frame signal for the current frame and the frame signal for the immediately preceding frame are simply overlapped, discontinuity may appear at the frame boundary. The discontinuity is caused due to a suppression process (or an amplification process) applied to adjacent frames based on different suppression (or amplification) coefficients G(f).
Such discontinuity at the frame boundary causes noise, which is very uncomfortable to the ear of the listener.
As a method for solving this problem, for example, there is a method proposed in Patent Document 1. In the method proposed in Patent Document 1, for example, overlapping is performed after making the amplitudes at both ends of the frame signal by attaching a DC component, to solve the problem of discontinuity at the frame boundary.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2008-58450